1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotography technique, such as a copying machine, a facsimile machine or a printer, which forms a toner image on an image holder such as a photosensitive drum and transfers the toner image onto a recording medium, by means of electrostatic attraction.
2. Description of the Related Art
In an image forming apparatus which forms a toner image on an image holder such as a photosensitive drum and transfers the toner image onto a recording medium such as paper, when the apparatus is stopped due to a paper jam or the like, nonfixed toner remains on a photosensitive drum 1 as shown in FIG. 7. In FIG. 7, numeral 2 denotes a transfer belt and numeral 6 a charge roller for charging the transfer belt 2. Since the photosensitive drum 1 can not stop its rotation immediately upon stoppage of the apparatus due to its inertia, a remaining range of the nonfixed toner becomes correspondingly large. Thus, when restarting the apparatus, the nonfixed toner on the photosensitive drum 1 is separated and recovered by means of a cleaner at a downstream side relative to the rotation of the photosensitive drum 1.
However, if such a cleaning operation is performed every time the apparatus is restarted, a large load is applied to a blade of the cleaner so that a stable cleaning effect can not be ensured.
In view of this, Japanese Laid-open (unexamined) Patent Publication No. 5-119635 proposes a technique wherein, as shown in FIG. 8, when an image forming apparatus is restarted, a transfer belt 2 is caused to abut upon a photosensitive drum 1 and current (although there is no particular explanation in the foregoing publication, it is considered from a context that a value of the current is approximately equal to a value of transfer current which is supplied upon image formation on a recording medium) is fed to a transfer charger such as a charge roller 6 for giving charge to the transfer belt 2. Thus, the foregoing nonfixed toner on the photosensitive drum 1 is transferred onto the transfer belt 2 and then removed by a cleaner of the transfer belt 2 at a downstream side thereof, while residual toner on the photosensitive drum 1 after the transfer is recovered by a cleaner of the photosensitive drum 1. Thus, a load applied to the cleaner of the photosensitive drum 1 is reduced. The residual toner recovered by the cleaner of the photosensitive drum 1 is subjected to removal of charge and then returned to a developing unit so as to be recycled for developing a latent image on the photosensitive drum 1.
However, in the image forming apparatus wherein toner at the developing unit is always in contact with the photosensitive drum, the toner flows out onto the photosensitive drum due to the rotation of the photosensitive drum upon restarting the apparatus even if charge is not applied to the developing unit. The technique of the foregoing publication can not prevent such flowing-out of the toner upon restarting the apparatus.
Further, when the restart of the apparatus due to a paper jam is carried out, paper powder invades the nonfixed toner on the photosensitive drum. The nonfixed toner mixed with the paper powder is separated from the photosensitive drum by the cleaner of the photosensitive drum. However, the nonfixed toner mixed with the paper powder significantly increases abrasion of a blade of the cleaner, thereby to cause replacement thereof and shorten the life duration of the photosensitive drum.
Further, if the toner returned from the cleaner of the photosensitive drum to the developing unit for recycling contains the paper powder, charging of the toner is adversely affected to induce an adverse effect on the print quality.